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Speaking of Precision

Speaking of Precision is a knowledge preservation and thought leadership blog covering the precision machining industry, its materials and services. With over 36 years of hands on experience in steelmaking, manufacturing, quality, and management, Miles Free (Milo) Director of Industry Research and Technology at PMPA helps answer "How?" "With what?" and occasionally "Really?"

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Adjusting to Unleaded-In Brass

Posted February 10, 2015 12:30 PM by Milo
Pathfinder Tags: brass lead machining

Unleaded brasses are not necessarily harder to run than leaded brass. They are just different. By recognizing and accommodating for their lack of Lead, and the resultant different thermal conductivity, differences in chip forming, and the need to up-tool for heavier feeds rather than higher speeds, your shop can also be successful at making parts from these newer, more challenging grades.

Same yellow color, just no Lead in the grain boundaries

It is widely established that Lead promotes machinability. To get the maximum production from automatic machines, additions of Lead have been commonly used in metals, particularly steels and brasses. In brass, dispersed in the grain boundaries, Lead acts as an internal lubricant- it reduces friction, and thus heat. By reducing the heat, Lead allows the metals to which it has been added to be machined at much higher speeds than the comparable non-leaded grades. These higher speeds [rpm or surface feet per minute (sfm)] result in shorter cycle times to produce each part. Short cycle times mean less expensive parts.

Leaded Brass offered these historical advantages

  • Excellent surface finish
  • Forgiving of machine mis-adjustments
  • No thermal issues
  • Fast cycle times
  • No chip control issues

When machining non leaded materials, we have to somehow maintain surface finish, get to commercially feasible cycle times, and deal with less than ideal chip characteristics.

What are some strategies for machining the new unleaded brasses?

Increase the feed. Since we lost the lead and the ability to run at higher speeds, increasing the feed can help us get to equivalent cubic inches of removal rates.

Improve the machine rigidity. Heavier feeds mean that your machine needs to be adjusted and solid. It also means more horsepower required- again mandating a rock-solid setup.

Improve the tool. 4 % lead is very forgiving of tool quality; The new nonleaded grades are the opposite, they present a number of challenges to your tools. Improved materials, geometry and coatings are key to machining unleaded brasses with minimum issues. also, they will require fewer replacements, helping to get more net production at the end of the shift.

Improve the chip management. some unleaded grades replace the lead with zinc, resulting in a grade with a type III chip- stringy and birds-nest prone. With these grades payespecioal attention to drills selected, and try inserts with chip control features to help you manage that chip.

Deal with the increased heat. The Lead helped to reduce friction and heat in the Leaded grades. with the lead removed, you will have increased heat generated. Carbide is more forgiving of heat, as are tool coatings. Talk to your supplier of Metal working fluids- Chances are that they will have a fluid that will help manage thiose extra BTU's and maintain your tools' edges.

Change your ideas about machining brass. unleaded brass machines more like steel than brass. as long as you think of it like leaded brass you will fight it. instead, think of it as just a yellow version of 1215 steel or stainless and your expectations will be much closer to reality.

Our cheat sheet for moving from leaded steel to unleaded steel provides a roadmap for adjusting to unleaded brass

Unleaded brasses are not necessarily harder to run than leaded brass. They are just different. By recognizing and accommodating for their lack of Lead, and the resultant different thermal conductivity, differences in chip forming, and the need to up tool for heavier feeds rather than higher speeds, your shop can also be successful at making parts from these newer, more challenging grades.

The market for our precision machined parts continues to be evolve. Evolve your thinking and processing to adjust to the realities of unleaded materials to remain a viable and preferred supplier.

For more details on grades and recommendations, read our article Adjusting to Unleaded.


Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which you can also read here.

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#1

Re: Adjusting to Unleaded-In Brass

02/10/2015 2:07 PM

I know next nothing about machining, so I am allowed to ask a stupid question. Is monitoring of the cutting action ever done? When I say monitoring, I mean such as acoustic and temperature feedback from the bit/holder and drive torque.

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Re: Adjusting to Unleaded-In Brass

02/10/2015 2:55 PM

Not on routine machining. Some firms that machine lights out (unattended/lightly attended) may have broken tool detection but the kind of acoustic systems that you mention are VERY RARE. Temperature feedback is too slow to be actionable; drive torque may be considered by a controller as part of an embedded detection/ alarm automatic shutdown scheme.

Milo

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Re: Adjusting to Unleaded-In Brass

02/10/2015 3:17 PM

Milo,

Thanks for the getback. The reason I asked, is my grandfather was a master machinist and I remember him telling me you had to "listen to your machine and it will tell you what is going on".

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Re: Adjusting to Unleaded-In Brass

02/10/2015 3:26 PM

your grandfather was indeed a master. Listening for overtones, harmonics, vibrations, chatter and the like is indeed a lost art.

Milo

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Re: Adjusting to Unleaded-In Brass

02/10/2015 4:30 PM

In deed it is an art. The sensory feedback from a precision machine tool to a skilled and experienced machinist is a long way from being replicated by a computer.

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Re: Adjusting to Unleaded-In Brass

02/10/2015 7:12 PM

Modern CNC machining centers can cut to perfection, but if a human is turning the cranks the look, sound and feel of the equipment is most important. Tool grinding lathe tools is itself an art.

Feed rate is critical. I've never run CNC, but I have broken drills, taps and gouged round stock in my day.

As Miles says, each material has its own personality, just like a woman.

Learning to handle the different materials is as essential to good machining as proper lubrication.

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